Remove hardcoded paths to commands on the host machine

Synapse v.1.14.0

Depending on the distro, common commands like sleep and chown may either
be located in /bin or /usr/bin.

Systemd added path lookup to ExecStart in v239, allowing only the
command name to be put in unit files and not the full path as
historically required. At least Ubuntu 18.04 LTS is however still on
v237 so we should maintain portability for a while longer.

fix for importing sqllite database

the current version fails the import, because the volume for the media is missing. It still fails if you have the optional shared secret password provider is enabled, so that might need another mount. Commenting out the password provider in the hoimeserver.yaml during the run works as well.

Clarify documentation on port forwarding of Jitsi/TRP behind NAT

to prevent docker from using dir instead of file

Using the older one likely leads to issues like #517.

added docs, added seperate service for database, pr comments

better path handling, fixed some mistakes

Fix/mx puppet bridge

Update postgres (12.2 -> 12.3, etc)